[subprocess] coverage and read-only site-packages #2084
Description
Describe the bug
Patching read-only site-packages for subprocess support fails.
To Reproduce
If coverage runs in environments where Python's site-packages are read-only the patch=subprocess feature doesn't work. Errors of creating pth files are ignored:
https://github.com/coveragepy/coveragepy/blob/main/coverage/patch.py#L156-L165
Answer the questions below:
- What version of Python are you using?
Python 3.13.9 - What version of coverage.py shows the problem? The output of
coverage debug sysis helpful.
-- sys -------------------------------------------------------
coverage_version: 7.11.3
coverage_module: /usr/src/.local/lib/python3/site-packages/coverage/__init__.py
core: -none-
CTracer: available from /usr/src/.local/lib/python3/site-packages/coverage/tracer.cpython-313-x86_64-linux-gnu.so
plugins.file_tracers: -none-
plugins.configurers: -none-
plugins.context_switchers: -none-
configs_attempted: /usr/src/RPM/BUILD/pyproject_installer/.coveragerc
configs_read: /usr/src/RPM/BUILD/pyproject_installer/.coveragerc
config_file: /usr/src/RPM/BUILD/pyproject_installer/.coveragerc
config_contents: b'[run]\npatch = subprocess\n'
data_file: -none-
python: 3.13.9 (main, Nov 9 2025, 20:22:19) [GCC 14.3.1 20251017 (ALT Sisyphus 14.3.1-alt2)]
platform: Linux-6.12.56-6.12-alt1-x86_64-with-glibc2.40
implementation: CPython
build: main
Nov 9 2025 20:22:19
gil_enabled: True
executable: /usr/bin/python3
def_encoding: utf-8
fs_encoding: utf-8
pid: 2752394
cwd: /usr/src/RPM/BUILD/pyproject_installer
path: /usr/src/.local/bin
/usr/src/RPM/BUILD/pyproject_installer/src
/usr/lib64/python313.zip
/usr/lib64/python3.13
/usr/lib64/python3.13/lib-dynload
/usr/src/.local/lib/python3/site-packages
/usr/lib64/python3/site-packages
/usr/lib/python3/site-packages
environment: COVERAGE_PROCESS_CONFIG = eyJjb25maWdfZmlsZXNfYXR0ZW1wdGVkIjogWyIvdXNyL3NyYy9SUE0vQ...
COVERAGE_PROCESS_START = .coveragerc
HOME = /usr/src
PYTHONPATH = src
command_line: /usr/src/.local/bin/coverage debug sys
time: 2025-11-12 14:05:05
- How to reproduce
- install any Linux distro
- install coverage (e.g. with pip into user sitepackages)
- run coverage with
patch = subprocess
$ coverage run --debug=patch -m pytest -vra
Patching subprocess
Writing subprocess .pth file: '/usr/lib64/python3/site-packages/subcover_2636615.pth'
Writing subprocess .pth file: '/usr/lib/python3/site-packages/subcover_2636615.pth'
- Actual result
Files are not created, subprocess coverage is not measured.